The present invention relates to a system for verifying the authenticity of documents such as checks wherein a field of photoactive microcapsules containing a radiation sensitive internal phase is provided in a localized area on one or more faces of the document and image-wise exposed to produce a latent image which is developed upon presenting the document and used to verify its authenticity.
Various systems have been developed for authenticating documents but none are particularly convenient for use in authenticating checks and the like which are negotiated by signatures which often cannot be immediately verified. For example, U.S. Pat. No. 3,001,887 to Ahlem, Jr. et al (1961) discloses a system for authenticating documents such as raffle tickets wherein fine colloidal silica is presented on the document in the form of an invisible latent image and the document is authenticated by applying to the surface of the document a colorless reactant such as a color former which reacts with the silica and produces a colored image which can be used to check the validity of the ticket.
U.S. Pat. No. 4,037,007 to Wood (1977) discloses a paper for security documents such as bank checks which contain planchettes which contain one or more color formers wherein the documents are authenticated by the addition of reactants which cause the planchettes to change color.
U.S. Pat. No. 4,360,543 to Skees et al (1982) discloses a method for producing a hidden image by applying to a document surface a colorless ink in the configuration of an image. This ink is overcoated with an encapsulated reactant which is capable of reacting with the ink to form color. The document is authenticated by applying pressure to the encapsulated reactant which causes it to be released from the microcapsules and react with the ink whereupon the hidden image is revealed.